Assessment of the occupational exposure to cobalt at a base metal refinery

Abstract

Objectives: The objectives for this study were (i) to assess the respiratory exposure of base metal refinery workers to cobalt sulphate; (ii) to assess the dermal exposure of these workers to cobalt sulphate; (iii) to assess the skin barrier function by means of TEWL, skin hydration and skin surface pH; (iv) to assess workers’ urine cobalt concentration by means of biological monitoring and; (v) to determine the contribution of each exposure route to the total urine content. Methods: The study was conducted at a base metal refinery where workers stationed in a Cobalt plant (20 workers) and Packaging plant (5 workers) are potentially exposed to soluble cobalt sulphate through respiratory and dermal exposure routes. Evaluation of the respiratory exposure was quantified using the Institute of Occupational Medicine (IOM) aerosol sampler. Evaluation of the dermal exposure included quantification of the cobalt deposition on the skin using Ghostwipes™ as a removal method, while TEWL, skin hydration and pH measurements were used to determine the change in skin barrier function. Dermal measurements were done on four different anatomical areas (forearm, wrist, palm of hand and back of hand) before, during and after the working shift. Evaluation of the cobalt content in the urine of employees was included to evaluate the exposure through all exposure routes (respiratory and dermal). Results and Discussion: Occupational exposure to cobalt at a base metal refinery was detected through the respiratory and dermal routes of exposure. High inhalable airborne exposures above the Occupational Exposure Limit - Time Weighted Average (OEL-TWA) were noted for several workers in both the Cobalt and Packaging plant of the base metal refinery. Respirable fractions only contributed a small fraction of the total airborne exposure to cobalt. Detectable levels of cobalt were found on the skin of exposed workers in both the Cobalt and Packaging plant with geometric means ranging between 0.104 μg/cm2 on the back of hand and 77.600 μg/cm2 on the wrist. The majority of measurements indicated an increase in TEWL percentage changes from the beginning to the end of the shift, with a decrease being reported in all skin hydration measurements, and pH indicating high variability between the Cobalt and Packaging plant. Biological monitoring data indicated baseline urine levels above the Biological Exposure Index (BEI) of 15 μg Co/g Creatinine in five out of the 12 workers in the Cobalt plant. The mean urine cobalt concentration in Cobalt plant workers decreased slightly from a baseline measurement of 17.83 μg Co/g Creatinine to 12.37 μg Co/g Creatinine on day 5. Workers’ urine levels in the Packaging plant however indicated cobalt concentrations of approximately three times lower than the recommended BEI, with levels ranging between a baseline measurement of 2.5 μg Co/g Creatinine and 6.6 μg Co/g Creatinine on day 5. Pair wise correlations indicated significant strong positive correlations between dermal exposure and biological monitoring (change in urine cobalt concentration between Day 3 and the Baseline) in the Cobalt plant and the Cobalt and Packaging plants combined. Conclusion: Refinery workers are exposed to cobalt sulphate (liquid solution and cobalt sulphate crystals) through the respiratory and dermal routes of exposure in both the Cobalt and Packaging plant of the base metal refinery, of which only dermal exposure significantly correlated with the total urine content of the workers. Changes in the skin barrier function also indicated that the skin integrity was compromised.